Current trends suggest that data center architectures are evolving in that the network is envisioned to contain a large number of servers, both physical and virtual and the server-to-server traffic (east-west) is expected to dominate the traffic from the internet (north-south). Typically, servers are organized into a set of PODs. The interface toward a POD may be referred to as a Top-Of-Rack switch (“ToR”). The ToRs themselves are then interconnected hierarchically via a switch-fabric so that any server should be able to communicate with any other server. As the size of the data center goes up, scalability is one of the most prominent requirements where any-to-any communication should still be possible without large scale changes to the network infrastructure.
While having a large flat layer 2 network allows for the most “agility”, such a network suffers from the serious drawback of serving as a single broadcast domain. Consequently, flooding, multicasts, and broadcasts are major problems since hosts may be un-necessarily bombarded. With IP becoming the de facto standard in data-centers, L3 ToR-based architectures are becoming increasingly common. Consequently, the bottle-neck in the ToR now shifts from the size of the MAC table to the FIB/Adjacency (next-hop) tables that are employed for IP routing. For purposes of the present disclosure it may be assumed that a vlan corresponds to a unique IP subnet.
In order to have the most flexibility in terms of resource allocation based on changing demand, there exists a need for data center providers to provision a subnet/vlan in any ToR. However, if a subnet spans multiple ToRs, then the any-to-any communication requirement will require ToRs to maintain a /32 address entry in the FIB tables for every host in the data center. As such there is a further need to effectively utilize the FIB tables on the individual ToRs while still satisfying the any-to-any communication requirement without compromising on the agility aspect.